Multimode radio communication system

ABSTRACT

Like a conventional one-way pager system, a two-way pager system is provided in which a message is received by paging from a base station and a message responding to the received message is returned to the base station. In this system, direct communication and peer-to-peer communication between terminals are performed. All the terminals included in the service area of the base station are always synchronized with sync signals paged from the base station. No special infrastructure is therefore required for synchronizing the terminals with the sync signals to perform the peer-to-peer communication. Furthermore, since each of the terminals receives a paging signal during the peer-to-peer communication, it can respond to a paging call.

RELATED APPLICATION

This Application is a divisional application from U.S. patentapplication Ser. No. 08/503,576, which was filed on Jul. 18, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multimode radio communication systemand, more specifically, to a multimode radio communication systemcapable of both indirect terminal-to-terminal communication performedthrough a base station and direct terminal-to-terminal communicationperformed not through a base station, for example, peer-to-peercommunication.

2. Description of the Related Art

An example of radio communication system, is a pager system wherein abase station having a transmitting antenna of 100 meters or more inheight is provided within every service area whose radius is about 30kilometers. To call a specified terminal (pager) holder in this system,a caller dials the calling number of a pager of the terminal holder bytelephone. In response to the calling number, a service center of apager service company makes all the base stations send forth the callingnumber at once (or page the calling number). Upon receiving the callingnumber, the pager gives a calling sound to inform the terminal holder ofthe call. Recently a pager system capable of transmitting a message aswell as a calling number, has been developed, in which not only is acalling sound produced but a message is displayed on a display of aterminal.

In either case, however, since the prior art pager system is directed toone-way communication from a base station to a terminal, anothercommunication system, such as telephone, has to be employed when acalled party wishes to respond to a received calling number or areceived message. To eliminate this problem, a two-way pager system (orbidirectional pager system) capable of transmitting a response messagefrom a terminal (pager) to a base station, has recently been developed.

According to one proposal of the two-way pager system, the samecommunication system as that of the normal one-way pager system is usedin the down link from the base station to the pager, while acommunication system different from that of the one-way pager system isadopted in the up link from the pager to the base station, as describedin U.S. Pat. No. 5,335,246. The two-way radio communication between twopagers is achieved as follows: A transmission message is transmittedfrom one of the pagers to a service center of a pager service companyusing an up link through a base station. The service center makes allbase stations transmit the transmission message at once (or page)through the down links. Upon receiving the transmission message, theother pager transmits a response message to the base station through theup link and then to the service center, as described above. The servicecenter returns the response message to the former pager via the basestation using the down link.

Moreover, there are a portable telephone system and a mobile telephonesystem as other radio communication systems for achieving two-waycommunication.

The foregoing communication systems are all based on the premise of theuse of service provider infrastructure equipment such as base stationsand telephone lines. Therefore, even when two terminals for two-waycommunication are close to each other and no infrastructure equipment isrequired, a signal always has to be transmitted via both a base stationand a service center, with the result that the time for communicationbetween the two terminals is lengthened and the infrastructure equipmentruns to waste.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amultimode radio communication system capable of terminal-to-terminalcommunication, i.e., peer-to-peer communication, performed without usingany infrastructure equipment, as well as two-way radio communicationperformed using infrastructure equipment.

A related object of the present invention is to provide a multimoderadio communication terminal capable of terminal-to-terminalcommunication, i.e., peer-to-peer communication, performed without usingany infrastructure equipment, as well as two-way radio communicationperformed using infrastructure equipment.

A further object of the present invention is to provide a base stationused for a multimode radio communication system capable ofterminal-to-terminal communication, i.e., peer-to-peer communication,performed without using any infrastructure equipment, as well as two-wayradio communication performed using infrastructure equipment.

A still further object of the present invention is to provide amultimode radio communication method capable of terminal-to-terminalcommunication, i.e., peer-to-peer communication, performed without usingany infrastructure equipment, as well as two-way radio communicationperformed using infrastructure equipment.

According to the present invention, there is provided a multimode radiocommunication system comprising a base station connected to a wirecommunication network, the base station transmitting a sync signal; anda plurality of radio communication terminals wirelessly connected tosaid base station, said plurality of radio communication terminals beingoperated in synchronization with the sync signal transmitted from saidbase station, and a first radio communication terminal of said pluralityof radio communication terminals indirectly communicating with a secondradio communication terminal thereof through said base station ordirectly communicating with the second radio communication terminal insynchronization with the sync signal.

According to the present invention, there is provided a radiocommunication terminal comprising means for receiving a sync signaltransmitted from a base station connected to a wire communicationnetwork; and means for directly communicating with another radiocommunication terminal by a peer-to-peer communication system insynchronization with the sync signal without using the base station.

According to the present invention, there is provided a base stationcommunicating with radio communication terminals, comprising means forreceiving signals from the radio communication terminals; means fordetecting positions of the radio communication terminals based on thesignals received by said receiving means; means for producing a linkprediction parameter indicating whether or not there is a peer-to-peercommunication between the radio communication terminals based on thepositions of the radio communication terminals; and means fortransmitting the link prediction parameter to the radio communicationterminals.

According to the present invention, there is provided a radiocommunication method for a radio communication terminal, comprisingsteps of receiving a sync signal transmitted from a base station; andexecuting a peer-to-peer communication with another radio communicationterminal in synchronism with the sync signal without using the basestation.

Since the multimode radio communication system of the present inventionallows communication without using infrastructure equipment as well ascommunication using infrastructure equipment, the infrastructureequipment can effectively be utilized, and new infrastructure equipmentis not always required. The use of infrastructure equipment may imposerestrictions such as communication speed and communication capacity onthe system. These restrictions can be removed if communication isexecuted without using any infrastructure equipment.

Additional objects and advantages of the present invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the present invention.The objects and advantages of the present invention may be realized andobtained by means of the instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe present invention and, together with the general description givenabove and the detailed description of the preferred embodiments givenbelow, serve to explain the principles of the present invention inwhich:

FIG. 1 is a block diagram of a multimode radio communication systemaccording to a first embodiment of the present invention;

FIG. 2 is a schematic view of peer-to-peer communication and SSFHcommunication used in an up link of two-way pager communicationaccording to the present invention;

FIG. 3 is a block diagram showing a multimode radio communicationterminal according to the first embodiment;

FIG. 4 is a timing chart showing the operation of the multimode radiocommunication system according to the first embodiment;

FIG. 5 is a schematic view of a frequency multiplex communication systemas an example of multiplex communication system according to the firstembodiment;

FIG. 6 is a schematic view of a time multiplex communication system asanother example of multiplex communication system according to the firstembodiment;

FIG. 7 is a schematic view of still another example of a multiplexcommunication system according to the first embodiment;

FIG. 8 is a timing chart showing an operation of a multimode radiocommunication system according to a second embodiment of the presentinvention;

FIG. 9 is a block diagram showing the entire constitution of a radiocommunication system according to a third embodiment of the presentinvention;

FIG. 10 is a flowchart showing the first half of the operation of thethird embodiment;

FIG. 11 is a flowchart showing the second half of the operation of thethird embodiment;

FIG. 12 is a view showing a radio communication system according to afourth embodiment of the present invention;

FIG. 13 is a block diagram showing the entire constitution of a radiocommunication system according to a fifth embodiment of the presentinvention;

FIG. 14 is a block diagram showing a radio communication terminalaccording to the fifth embodiment;

FIG. 15 is a flowchart showing the first half of the operation of thesystem according to the fifth embodiment;

FIG. 16 is a flowchart showing the second half of the operation of thesystem according to the fifth embodiment;

FIG. 17 is a view showing a radio communication system according to asixth embodiment of the present invention;

FIG. 18 is a block diagram showing the constitution of a relay stationof the radio communication system according to the sixth embodiment;

FIG. 19 is a view of the constitution of the radio communication systemaccording to the sixth embodiment wherein a signal is transmitted via aplurality of relay stations;

FIG. 20 shows data transitions when a signal is transmitted via a relaystation;

FIG. 21 shows the data structure at the relay station; and

FIG. 22 shows code format according to a modified embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a multimode radio communication systemaccording to the present invention will now be described with referenceto the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing the entire constitution of a multimoderadio communication system according to a first embodiment of thepresent invention. A two-way pager system capable of peer-to-peercommunication will now be described as the first embodiment.

A plurality of terminals (pagers), for example, two pagers 18 a and 18 bare present within a service area of a base station 10 connected to aservice center through a wire telephone network (not shown). A number ofbase stations are connected to the service center, though not shown. Thebase station 10 includes a transmitter 12, a receiver 14, and a controlcircuit 16. The transmitter 12 pages the pagers 18 a and 18 b. The samecommunication system as a commonly-used one-way pager system is adoptedin the down links from the base station 10 to the pagers 18 a and 18 b.Such a down-link communication system comprises a POCSAG (Post OfficeCode Standardization Advisory Group) system (CCIR Rec. 584), a GSC(Golay sequential Code) system (CCIR Rec. 900), an NTT (Nippon Telegraph& Telephone Company) system, and the like. The POCSAG system is adoptedin this embodiment, though any of these can be done.

The receiver 14 of the base station 10 receives transmission signalsfrom the pagers 18 a and 18 b. A communication system different from theone-way pager system is adopted in the up links from the pagers 18 a and18 b to the base station 10. The up-link communication system comprisesthe same digital communication system as a conventional two-waycommunication system and a spectrum spreading communication system usingan ISM (Industrial Scientific Medical) band which was widely open towireless LAN in the United States and Europe and is considered to beeasily employed. This spectrum spreading communication system is moreresistant to interference than a frequency-division multiplexing systemon a time-division multiplexing system and thus is widely used. Thespectrum spreading communication system is roughly divided into a directspreading system and a spread spectrum frequency hopping (SSFH) system.While the direct spreading system is a system of spreading informationin the form of frequency (spectrum) by a code having orthogonality, theSSFH system is a system of transmitting a signal by varying (hopping)its frequency as time passes. By selecting any one of preset frequenciesat predetermined time, both the transmission and reception areperformed. To do this, information of the predetermined time and thepreset frequencies must be held in each of the transmitting andreceiving terminals. Since any frequency can be selected at thepredetermined time, the communications corresponding to the usablenumber of frequencies can be performed at once. If the predeterminedtime is divided, the number of simultaneously communicable terminals canbe increased.

If the frequency of the SSFH system is fixed to the single frequency,the SSFH system is equivalent to the conventional two-way communicationsystem. Therefore, the above description can be also applied to theconventional two-way communication system and the conventional two-waycommunication system can be used for the up-link communication systeminstead of the SSFH system.

In the following description, the SSFH system is employed. However, itis possible to use the direct spreading system for the up-linkcommunication system.

FIG. 2 shows the principle of the SSFH system described above. Referringto FIG. 2, any one of the frequencies f₁ to f₅ is selected whenever afixed period of time elapses. After time t₇, a pattern of frequencyvariations from t₁ to t₇ is repeated.

If the transmitting terminal and the receiving terminal have the samefrequency hopping timing (t₁) and the same frequency hopping pattern, itis possible to demodulate the transmitting signal at the receivingterminal. In order to execute a SSFH communication system, it isnecessary to make the frequency hopping pattern of the transmittingterminal equal to that of the receiving terminal. There are two methodsfor making the frequency hopping pattern of the transmitting terminalequal to that of the receiving terminal. According to one method, thesame frequency hopping pattern is previously set to the transmittingterminal and the receiving terminal. Alternately, it is possible to seta plurality of frequency hopping patterns to the transmitting terminaland the receiving terminal. In the latter case, it is necessary toinform the receiving terminal of information as to which frequencyhopping pattern is selected before the start of communication. In thefollowing description, the former method is employed. However, it ispossible to employ the latter method. If the latter method is employed,it is necessary to transmit a parameter signal from the transmittingterminal to the receiving terminal before the start of communication,the parameter indicating which frequency hopping pattern is selected.

Returning to FIG. 1, the control circuit 16 receives a signal from theservice center through the telephone network and then supplies it to thetransmitter 12. The circuit 16 also supplies an output signal from thereceiver 14 to the transmitter 12 or the service center.

The constitution of the terminals 18 a and 18 b is illustrated in FIG.3. The terminals of the first embodiment feature two-way communicationbetween two terminals through the base stations and peer-to-peercommunication directly between them not through the base stations. It isassumed that the peer-to-peer communication is performed by the SSFHsystem as in the up link of the two-way pager communication. Asdescribed above, SSFH communication system is used for the peer-to-peercommunication system as well as the two-way pager system (up link).However, it is not necessary to use the same frequency hopping rate orthe same synchronization signal for the peer-to-peer communicationsystem and the two-way pager system (up link). Further, it is notnecessary to- use the same modulation rate for the peer-to-peercommunication system and the two-way pager system (up link).

Each terminal of the present invention includes an antenna 22 used forboth transmission and reception, and a transmission/reception selector24 is connected thereto. The selector 24 selects one of transmission andreception modes by means of a microcomputer 36. A signal received by theantenna 22 is sent to a mixer 26 via the selector 24. The mixer 26 issupplied with a predetermined oscillation signal from an oscillator 38.By controlling the microcomputer 36, the oscillator 38 outputs a signalhaving a predetermined frequency at the time of POCSAG communication(two-way pager communication in its down link), and outputs a signal,the frequency of which varies with the predetermined pattern as shown inFIG. 2 at the time of SSFH communication (two-way pager communication inits up link and peer-to-peer communication).

The mixer 26 converts a received high-frequency signal into anintermediate-frequency signal. The intermediate-frequency signal issupplied to a detector 30 via a BPF (band pass filter) 28 and subjectedto amplification, detection (FM detection), and determination. In thedetector 30, the signal is FM-detected and then demodulated into abinary data stream. An output signal of the detector 30 is supplied toan error correction circuit 32 and a sync detector 34. The circuit 32corrects an error on the basis of BCH codes and, more specifically, itcorrects an error based on the BCH (31, 21) system at the time of POCSAGcommunication (reception of two-way pager communication) and does anerror correction based on an error correction system suitable for theSSFH system at the time of SSFH communication (reception of peer-to-peercommunication) in response to a control signal supplied from themicrocomputer 36.

It is possible to correct an error by using the error correction methodbased on the BCH (31, 21) system at the time of SSFH communication.According to this modification, it is possible to reduce the errorcorrection circuit 32.

The output signals of error correction circuit 32 and sync detector 34are supplied to the microcomputer 36. A keyboard 54 and a display 56 areconnected to the microcomputer 36 through a man-machine interface 52.

Though it is possible to perform an error correction by means of themicrocomputer 36, the error correction circuit 32 is provided inaddition to the microcomputer 36 in order to clearly distinguish thefunctions of the error correction circuit 32 and the microcomputer 36.

The transmission signal output from the microcomputer 36 is sent tocoders 40 and 42. The coder 40 encodes data based on the two-way pagercommunication system in its up link at the time of transmission oftwo-way pager communication, while the coder 42 encodes data based onthe BCH (31, 21) system at the time of transmission of peer-to-peercommunication. The output signals of the coders 40 and 42 aretransmitted to a selector 48 through filters 44 and 46, respectively.Since a coding procedure is simple in its operation, it is possible toperform a coding procedure by means of the microcomputer 36. The filters44 and 46, which are preamplifiers for limiting the band of a modulatedsignal, shape the waveform of a data stream. The selector 48 selects anoutput of the filter 44 at the time of transmission of the two-way pagercommunication and selects that of the filter 46 at the time oftransmission of peer-to-peer communication. The output signal of theselector 48 is supplied to a direct modulator 50 to directly modulatethe output signal of the oscillator 38. The output signal of themodulator 50 is supplied to the antenna 22 via the selector 24. Themodulator 50 is always supplied with a signal whose frequency varieswith a predetermined pattern.

FIG. 4 is a timing chart of an operation of the multimode radiocommunication system of the first embodiment in which the POCSAGcommunication system is employed for the pager system. In the firstembodiment, the base station (paging station) P/T only transmits asignal and two terminals A and B both transmit and receive a signal.Hereinafter /T and /R indicate transmission and reception, respectively.The base station P/T transmits a preamble P and then a sync signal S ina fixed period. The cycle of the sync signal S is divided into aplurality of time slots, e.g., eight time slots 0 to 7. Any one of thetime slots 0 to 7 is assigned to each of the terminals in accordancewith a calling number, and paging reception (AIR, B/R) is performed onlywithin the assigned time slot. In this example, time slot 2 is assignedto the terminal A and time slot 6 is assigned to the terminal B. Inorder to perform paging reception only within the assigned time slot,these terminals are controlled so as to operate in synchronization withthe preamble P and sync signal S. The selector 24 usually selects thereception mode, the oscillator 38 oscillates the signal of thepredetermined frequency and the error correction circuit 32 corrects anerror based on the BCH (31, 21) system in order to receive the pagingsignal according to the POCSAG system. Usually, the terminal performs apaging reception operation only within the assigned time slot (time slot2 or 6) and the time slots for the preamble P and the sync signal S, andstops a paging reception operation during the other time slots in orderto reduce power consumption.

Each of the terminals includes time slots for peer-to-peer communicationsynchronized with the sync signal S. In this embodiment, two paging timeslots correspond to one peer-to-peer communication time slot. Forexample, when a user of terminal A wishes to start peer-to-peercommunication with terminal B, terminal A/T transmits message data toterminal B/R using a peer-to-peer communication time slot (“0” in thiscase) excluding its own paging time slot. The selector 24 selects atransmission mode, the coder 42 encodes the message data by the BCH (31,21) system, and the selector 48 selects an output signal of the filter46. The signal output from the selector 48 is SSFH-modulated by thedirect modulator 50, and the modulated signal is transmitted from theantenna 22 to the terminal B/R. Upon receiving the message data, theterminal B/T transmits response message data to the terminal A/R using apeer-to-peer communication time slot (“2” in this case) excluding itsown paging time slot. Similarly, data is transmitted and receivedbetween terminals A and B using peer-to-peer communication time slots.

Since terminals A and B are operated in response to the sync signal Ssupplied from the base station P/T, the synchronized peer-to-peercommunication can be achieved without any special synchronizing circuit.Since, furthermore, the peer-to-peer communication is performed using atime slot other than a paging time slot, the terminals can be operatedas a normal pager after the peer-to-peer communication is started. It isto be noted that the peer-to-peer communication slot is employed when aresponse message is transmitted to a base station in response to apaging signal from the base station. In this case, the start timing ofthe frequency hopping in an SSFH system begins at the end of the firstsync signal S following the preamble signal P.

As has been described above, the two-way pager terminals 18 a and 18 brespond to a paging signal and enable peer-to-peer communication withoutusing the base station. Consequently, a multimode radio communicationsystem capable of high-speed peer-to-peer communication can be attainedwithout increasing the load on infrastructure equipments.

Multiple access communication is suitable for peer-to-peercommunication, and an example thereof is illustrated in FIGS. 5 to 7.FIG. 5 shows an example of an FDMA (frequency division multiple access)system where the frequencies used for the communication vary fromterminal to terminal and between transmission and reception modes.Specifically, channels 1 and 2 are assigned to terminals 1 and 2,respectively, and channel 1 has transmission frequency f₁ and receptionfrequency f₂, while channel 2 has transmission frequency f₃ andreception frequency f₄. FIG. 6 shows an example of a TDMA (time divisionmultiple access) system where different frequencies are assigned toterminals and different transmission and reception time slots areapplied to each terminal. FIG. 7 shows an example of a TDD-TDMA systemwhere all terminals have the same frequency but time slots vary fromterminal to terminal or between transmission and reception modes. Aradio circuit can be effectively used by means of multiple accesscommunication. For example, a TDMA system may be used for the two-waypager system (up link) and an SSFH system at ISM band may be used forthe peer-to-peer communication system.

Second Embodiment

A multimode radio communication system according to other embodiments ofthe present invention will now be described. The same structuralelements as those of the first embodiment are denoted by the samereference numerals and their detailed descriptions are omitted. In thefirst embodiment, a terminal continues receiving a sync signal and isoperated to be in synchronism with the sync signal even afterpeer-to-peer communication is started, and it can receive a pagingsignal, whereas in the second embodiment, a terminal is completelyseparated from a base station after peer-to-peer communication isstarted.

FIG. 8 is a timing chart of the communication system of the secondembodiment. Terminal A/T transmits a peer-to-peer communication requestto a base station P/R via the up link of two-way pager communication. Ifan acknowledgment signal is returned to terminal A/R from the basestation P/T on the down link of the two-way pager communication, bothterminals A and B are operated to be in synchronism with a sync signalonly once. This sync signal establishes the frequency hopping starttiming of the SSFH system for the peer-to-peer communication. Then, aparameter for setting a channel is transmitted from terminal A/T toterminal B/R, and transmission/reception of data (peer-to-peercommunication) is started. In the example of FIG. 8, it is illustratedthat the terminals receive a sync signal transmitted from the pager basestation P/T during the peer-to-peer communication. However, as describedabove, it is not necessary to make the terminals receive the sync signalafter the start of the peer-to-peer communication. Upon completion ofthe communication, an end signal is transmitted from one of theterminals (terminal A/T in FIG. 8) to the base station P/R. In thesecond embodiment, too, the peer-to-peer communication is multiplexed.

Third Embodiment

The first and second embodiments assume that the peer-to-peercommunication can always be executed. Since, however, the terminals areportable and movable, the peer-to-peer communication cannot always bedone. According to the third embodiment, when peer-to-peer communicationis made impossible due to geographic conditions or the like, it isreplaced with two-way pager communication in which a signal istransmitted via a base station. Therefore, as shown in FIG. 9, thereceiver 14 of the base station 10 is provided with a position detector66 for detecting the position of a terminal. The position of a terminalis detected based on the phase and intensity of a received signal fromthe terminal. Such a detector is disclosed in U.S. Pat. No. 5,379,047,and U.S. Pat. No. 5,335,246, etc.

FIGS. 10 and 11 are flowcharts depicting peer-to-peer communication fromterminal “A” to terminal “B” in the system of the third embodiment. Instep #12, terminal “A” sends a peer-to-peer communication request to abase station. Upon acknowledging receipt of the request in step #14, thebase station detects a position of terminal “A” in step #16. In step#18, the base station informs terminal “B” of the peer-to-peercommunication request by paging. When detecting the paging in step #20,terminal “B” returns an acknowledgment signal to the base station instep #22. In step #24, the base station determines whether thepeer-to-peer communication is acknowledged by terminal “B”. If not, theflow returns to step #18, and paging is performed again. If it isacknowledged, the base station detects a position of terminal “B” instep #26.

In step #28, the base station simulates a radio channel for peer-to-peercommunication on the basis of the positions of terminals “A” and “B”. Itis then determined in step #30 whether the channel can be set up or notbased on the result of simulation. If it is determined the channel canbe set up, the base station sends parameters (information ontransmitting power, frequency, transmission start timing, transmissionright, a time period for which data can be transmitted or received,etc.) to terminals “A” and “B” to set up the radio channel in step #32.On the contrary, if it is determined that the channel cannot be set up,the base station sends the reason therefor to terminals “A” and “B” instep #34.

In steps #36 and #38, it is determined whether peer-to-peercommunication is possible or impossible in terminals “A” and “B”. If thecommunication is impossible, the reason therefor is displayed in steps#40 and #42, and two-way pager communication wherein data is transmittedvia the base station (step #48), is executed in steps #44 and #46. If itis determined that the peer-to-peer communication is possible, it isperformed in steps #50 and 52. The peer-to-peer communication ends ifone of the terminals “A” and “B” transmits an end code to the basestation in steps #58 and #60, and the base station detects the end codein step #62.

According to the third embodiment described above, when one of terminalsmakes a request for peer-to-peer communication, if the communicationcannot be performed because of positions of both the terminals, data canbe transferred between them by the two-way pager communication system,without unduly repeating a channel setting operation for thepeer-to-peer communication, with the result that infrastructureequipment can be effectively utilized in accordance with circumstances.

In the third embodiment, too, the peer-to-peer communication can bemultiplexed as shown in FIGS. 5 to 7.

When the request for peer-to-peer communication is rejected, it isreplaced with two-way pager communication using infrastructureequipment. However, one terminal oan transmit a request forcommunication with another terminal to a base station, withoutconsidering whether peer-to-peer communication or two-way pagercommunication is to be executed, and the base station may designate anappropriate communication mode in consideration of the relationship inposition between the terminals, the amount of transmission data, etc.and inform the terminals of the mode.

Fourth Embodiment

A method of detecting a position of a terminal in a multimode radiocommunication system according to a fourth embodiment of the presentinvention, will now be described. As is illustrated in FIG. 12, aplurality of receiving base stations, e.g., two receiving base stations72 and 74 in this embodiment are included in the service area of onetransmitting base station 70. The antenna directivity of each receivingbase station is divided into sectors. Each of the receiving basestations 72 and 74 detects which sector has received a signaltransmitted from a terminal 76. After considering the detection resultsof all the receiving base stations, the position of the terminal can bedetected by triangulation. The distance from each receiving base stationto its corresponding terminal can be approximately detected by measuringthe intensity of a received signal.

According to the fourth embodiment, each base station can detect itsterminal position with a simple arrangement.

Fifth Embodiment

FIG. 13 is a block diagram showing the entire constitution of a radiocommunication system according to a fifth embodiment of the presentinvention. In the third and fourth embodiments, a base station detects aposition of a terminal. However, in the fifth embodiment, a terminaldetects its own position. As shown in FIG. 13, the service area oftwo-way pagers (terminals) 82 a and 82 b includes one transmitting basestation 84 and a plurality of receiving base stations 86 and 88corresponding thereto. The transmitting base station 84 and receivingbase stations 86 and 88 are connected to a control circuit 90. Each ofthe terminals 82 a and 82 b detects its own position by a GPS (globalpositioning system) or other self-detection system for detecting theposition thereof without using other devices.

The constitution of each terminal is illustrated in FIG. 14. Theterminal of the fifth embodiment differs from that of the firstembodiment only in that a GPS 92 is added.

FIGS. 15 and 16 are flowcharts of an operation of the radiocommunication 'system according to the fifth embodiment. This flowchartis the same as that shown in FIGS. 10 and 11, directed to the thirdembodiment, except that a position of a terminal is detected not by abase station but by the terminal itself. In both the flowcharts, thesame steps are indicated by the same reference numerals. In the fifthembodiment, terminal “A” transmits a peer-to-peer communication requestand its own positional information to a base station in step #12A, thebase station receives the positional information of terminal “A” in step#16A, and terminal “B” transmits an acknowledgment signal and its ownpositional information to the base station in step #22A. The other stepsof the fifth embodiment are the same as those of the third embodiment.

In the fifth embodiment wherein a terminal detects its own position andtransmits it to a base station, too, the same advantage as that of thethird embodiment can be obtained.

Sixth Embodiment

In the foregoing embodiments, peer-to-peer communication is performedusing only two terminals. The radio communication system of the sixthembodiment comprises relay stations for peer-to-peer communication. FIG.17 shows the entire constitution of the system according to the sixthembodiment. Referring to FIG. 17, the service area of one transmittingbase station 102 includes a plurality of receiving base stations, i.e.,two receiving base stations 104 and 106 in this embodiment. The antennadirectivity of each receiving base station is divided into sectors inthe same manner as in the fourth embodiment. The receiving base stations104 and 106 detect which sectors have received signals transmitted fromterminals 108A, 108B and 108C. After considering the detection resultsof all the receiving base stations, the positions of the terminals canbe detected by triangulation. The distances between the receiving basestations and terminals can be approximately detected by measuring theintensity of received signals. Furthermore, a plurality of relaystations 110A, 110B and 110C for relaying peer-to-peer communicationbetween the terminals is provided. The base station simulates the radiochannel for peer-to-peer communication based on the positions of theterminals and determines whether or not a relay station is necessary forpeer-to-peer communication. If it is determined that a relay station isnecessary for peer-to-peer communication, the base station transmits aparameter signal indicating the positions of the terminals to the relaystation and a parameter signal indicating the address of the relaystation to the terminals. After a radio channel for relayingcommunication is set up, the terminals and the relay station areseparated from the base station. When the peer-to-peer communicationends, one of the terminals transmits an end code to the base station toinform the base station of the code of the peer-to-peer communication.

FIG. 18 is a block diagram showing a constitution of each of the relaystations 110A, 110B and 110C. Each relay station includes atransmitter/receiver 701 for transmitting/receiving a signal to/frombase stations (transmitting and receiving base stations), atransmitter/receiver 702 for peer-to-peer communication with anotherrelay station, a transmitter/receiver 703 for transmitting/receiving asignal to/from a terminal, and a controller 705 having a memory 706 forstoring a channel setting parameter and circumstances information forpeer-to-peer communication and a diversity processor 704 for executingdiversity processing. The controller 705 is connected to a pagingnetwork.

The antenna of the transmitter/receiver 702 of one relay station has adirectivity toward another relay station. In other words, if there are aplurality of relay stations, the antenna of the relay station isdirected to its target one.

Since, furthermore, the positional information of a terminal can bedetected, the transmitter/ receiver 703 for communicating with theterminal directs its antenna toward the terminal, with the result thattransmission/reception power can be decreased and interference ordisturbance can be lessened.

FIG. 19 shows the constitution of the system according to the sixthembodiment wherein a signal is transmitted via a plurality of relaystations. As shown in FIG. 19, a relay station 921 receives a signaldirectly from a terminal 932 and also receives a signal therefrom via arelay station 922. Based on these received signals, diversity processingis executed. In FIG. 19, reference numeral 901 denotes a transmittingbase station and reference numerals 931 and 933 indicate terminals.

FIG. 20 is a view of data transition when a signal is relayed by a relaystation. A signal transmitted from terminal “A” to a relay stationcontains a header, an address (transmission/reception), data, and FCS(error correction code). This signal is received by the relay station asit is. The relay station adds its address ADD_(R) to the received signaland sends it to terminal “B”n. The signal transmitted from the relaystation to terminal “B” thus contains a header, an address(transmission/reception), a relay station address data, and an FCS.

FIG. 21 is a view for explaining the structure of data at a relaystation and, in this case, TDMA is employed as a communication system.The amount (length) of transmitted data is arbitrarily determined andthen divided into frames each having a predetermined width. In otherwords, the number of frames varies with the amount of data. Each of theframes is divided into four slots. The three frames constitute one superframe. In the example of FIG. 21, data is divided into three frames. Thedata are assigned to the first slots (slots “a”) of each of the frames.

According to the aforementioned sixth embodiment, a relay station orstations are added to lengthen the distance between terminals capable ofpeer-to-peer communication and to enlarge the range in which thepeer-to-peer communication can be utilized.

The following advantages can be obtained from the above-describedmultimode radio communication system of the present invention:

(1) The communication between terminals, which was conventionallyperformed by a dedicated radio network, can be done by a peer-to-peercommunication system, without requiring any infrastructure.

(2) Since a base station recognizes the position of a terminal, it isable to judge whether peer-to-peer communication between terminals ispossible or impossible. No communication for setting a peer-to-peercommunication channel is needed between the terminals, thus improving incommunication efficiency. If a radio channel setting parameter forpeer-to-peer communication is transmitted to the terminals, or if aradio channel setting parameter is set to the terminals so as to preventmutual interference between the terminals, a number of users of theterminals can perform peer-to-peer communication in the same area,thereby improving in efficiency of use of peer-to-peer communication.

(3) Since a plurality of receiving base stations are provided, thepositions of terminals can be detected by triangulation from detectionresults of estimated positions of the terminals at the respective basestations.

(4) The relay function enhances the capability of peer-to-peercommunication and allows output signals of terminals to be collected onone relay station. Consequently, diversity processing can be executed,and the reliability, serviceability and convenience of the system areimproved.

(5) To lengthen the distance between terminals for peer-to-peercommunication, a relay radio device is provided, and it is provided witha directional antenna whose directivity is electrically variable. Thus,the transmission power between the relay device and terminals can bedecreased, the lifetime of batteries of the terminals can be lengthened,and a radio wave interference with other radio communication systems canbe reduced.

(6) The position of a terminal is acquired by an up link of a two-waypager system capable of peer-to-peer communication. The communicationsystem, frequency, transmission timing, transmission right, transmissiontime of the terminal for the peer-to-peer communication, are controlled.The frequency and timing necessary for the peer-to-peer communicationare transmitted to the terminal by a down link thereof. Consequently, anumber of terminals can perform the peer-to-peer communication, and avery convenient communication system can be achieved.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the present invention in its broaderaspects is not limited to the specific details, representative devices,and illustrated examples shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents. For example, a POCSAG system is used for a downlink of the two-way pager communication. However, there are othercommunication systems such as a FLEX (trademark) system which isdescribed in the U.S. Pat. No. 5,128,665 and is proposed by Motorola.FIG. 22 shows a data format of the FLEX system in which one cycle iscomprised of 128 frames. Each frame is comprised of a sync signal andeleven blocks. The terminal of the present invention is operated to bein synchronism with the sync signal and to generate an SSFH timingsignal.

What is claimed is:
 1. A radio communication terminal comprising: meansfor operating in synchronization with a sync signal transmitted from abase station connected to a wire communication network; means forcommunicating with said base station using a first time slot of aplurality of time slots, produced by a first time slot timing signal,said first time slot assigned to its own radio communication terminalfor communication with said base station; and means for communicating toanother radio communication terminal a communication originating at theradio communication terminal, said means for communicating includingmeans for transmitting a position information indicating the position ofthe terminal to said base station to inquire whether or not a directcommunication to the other radio communication terminal without usingthe base station is available to the base station using the first timeslot, means for controlling the direct communication to the other radiocommunication terminal when a first signal indicating that the directcommunication is available is received by the communicating means, andmeans for controlling an indirect communication to the other radiocommunication terminal via the base station when a second signalindicating that the direct communication is not available is received bythe communicating means.
 2. A radio communication terminal according toclaim 1, further comprising: means for detecting a position thereof; andmeans for transmitting the position thereof to the base station usingthe first time slot.
 3. A radio communication terminal according toclaim 1, further comprising: means for transmitting an end signal to thebase station using the first time slot when the direct communication isterminated.
 4. A radio communication terminal according to claim 1,wherein said radio communication terminal further comprises means fordetecting a position thereof.
 5. A radio communication terminalaccording to claim 1, wherein said first signal includes parameters toset up a radio channel between the radio communication terminals.
 6. Aradio communication terminal according to claim 1, wherein said directcommunication is a peer-to-peer communication and said indirectcommunication is a two-way pager communication.
 7. A radio communicationterminal according to claim 1, wherein the direct communication is witha time-division multiple access system.
 8. A radio communicationterminal according to claim 1, wherein the direct communication is witha frequency-division multiple access system.
 9. A radio communicationterminal according to claim 1, wherein the direct communication is witha time-division duplex/time division multiple access system.
 10. A radiocommunication terminal according to claim 1, wherein the indirectcommunication uses system infrastructure equipment.
 11. A base stationwhich communicates with radio communication terminals, comprising: meansfor receiving signals from the radio communication terminals; means fordetecting positions of the radio communication terminals based on thesignals received by said receiving means; means for receiving a requestto inquire whether a direct communication with a first one of the radiocommunication terminals without using the base station is available ornot from a second one of the radio communication terminals; means fordetermining whether or not the direct communication between the firstradio communication terminal and the second radio communication terminalis available based on the positions of the first radio communicationterminal and the second radio communication terminal; means fortransmitting a first signal to start the direct communication betweenthe first radio communication terminal and the second radiocommunication terminal when it is determined that the directcommunication is available; and means for transmitting a second signalto start an indirect communication between the first radio communicationterminal and the second radio communication terminal when it isdetermined that the direct communication is not available.
 12. A basestation according to claim 11, wherein said receiving means receives adirect communication request and a position signal indicating theposition of the first radio communication terminal from the second radiocommunication terminal.
 13. A base station according to claim 11,wherein said direct communication is a peer-to-peer communication andsaid indirect communication is a two-way pager communication.
 14. A basestation according to claim 11, wherein the direct communication is witha time-division multiple access system.
 15. A base station according toclaim 11, wherein the direct communication is with a frequency-divisionmultiple access system.
 16. A base station according to claim 11,wherein the direct communication is with a time-divisionduplex/time-division multiple access system.
 17. A base stationaccording to claim 11, wherein the indirect communication uses systeminfrastructure equipment.